Prune belly syndrome (PBS) is a rare congenital disorder that principally occurs in males and has the following three characteristic features:
Partial absence of some or most abdominal muscles
Urological abnormalities (eg, megaureter, hydroureter, hydronephrosis, vesicoureteral reflux, megacystis)
Pulmonary, orthopedic, cardiac, and gastrointestinal abnormalities may also be present. 
Frölich first described prune belly syndrome in 1839. In 1901, Osler gave the condition its name, which refers to the wrinkled appearance of the abdomen resulting from the muscular deficiency. Prune belly syndrome is also called Eagle-Barrett syndrome, Obrinsky syndrome, and triad syndrome. [2, 3]
The treatment of prune belly syndrome poses a significant problem to pediatric urologists. Some authors call for conservative management of the urinary tract in boys with prune belly syndrome, while others advocate an aggressive approach, operating on patients aged 10 days.
No definitive timing for treatment of prune belly syndrome has been substantiated. Pediatric urologists have observed that boys with prune belly syndrome can present with a spectrum of abnormalities. At one end of the spectrum, the condition may cause severe urogenital and pulmonary problems incompatible with life (resulting in stillbirth); at the other end of the spectrum, the condition may cause few, if any, urological abnormalities that require no treatment other than orchidopexy to correct the undescended testis. The decision to aggressively treat the urinary tract in these children should be based on the clinical presentation and not solely on radiographic appearance.
Children with prune belly syndrome can present with myriad renal, ureteral, and urethral abnormalities. Obstruction and/or upper urinary tract dilatation is not unusual in these children. The site of obstruction can vary from as high as the pelviureteral junction to as low as the prostatic membranous urethra.
A lack of abdominal muscles leads to a poor cough mechanism, which, in turn, leads to increased pulmonary secretions. Weak abdominal muscles lead to constipation because of an inability to perform the Valsalva maneuver, which helps push the stool out of the rectum during defecation.
In a review of 46 patients (44 boys and 2 girls) with prune belly syndrome seen at a pediatric urology clinic, the following were the most common clinical manifestations  :
Hydroureteronephrosis – 97.8%
Vesicoureteral reflux – 78.3%
Significant pulmonary insufficiency – 10.9%
Congenital malformations – 39.1%
Chronic kidney disease – 39.1%; 17.4% underwent renal transplantation
The mortality rate associated with prune belly syndrome is 20%.
Prune belly syndrome affects 1 per 30,000-40,000 live births. Approximately 3-4% of all prune belly syndrome cases occur in females. Twinning is associated with prune belly syndrome; 4% of all cases are products of twin pregnancies.
In 1903, Strumme proposed that prune belly syndrome may be caused by in utero bladder obstruction, stating that dilatation of the urinary tract in utero leads to secondary-pressure atrophy of the abdominal wall and the subsequent clinical findings. More recent theories focus on a functional obstruction due to prostatic hypoplasia that leads to a conformational change in the prostatic urethra during voiding, thereby causing obstruction. The most recent theories suggest a transient obstruction at the junction of the glanular and penile urethra. This would explain the high incidence of megalourethra observed in cases of prune belly syndrome.
Considering current knowledge regarding high-pressure voiding and reflux, the theories involving urethral abnormalities can also explain the upper tract deformities that this syndrome can cause. High-pressure voiding has been discovered to lead to reflux in patients without prune belly syndrome. The obstructive process that occurs may impart a similar effect that mimics the dyssynergic voiding in persons with reflux. This high-pressure voiding thereby leads to changes in the location of the ureter, as well as the deleterious effects of the water-hammer effect on the renal tissue. Therefore, this abnormal high-pressure voiding process could explain reflux that is encountered along with renal dysplasia. The overdistended bladder could result in the abnormal development of the abdominal wall musculature and prevent the descent of the testis.
The histopathology of the abdominal wall muscles demonstrates a pattern of developmental arrest rather than one of atrophy. This is also suggested by a lack of any aponeurotic layers.
Fetal ascites, which may be transient because the urine is reabsorbed before birth, may explain the abdominal wall defects.
The prevailing theory is mesodermal arrest, which would explain the involvement of the genitourinary tract, the testis, and the abdominal wall. A noxious insult would have to occur between the 6th and 10th weeks of gestation. Some place the insult at 3 weeks of embryogenesis, which may explain the prostatic hypoplasia and poor glandular development.
The mesodermal arrest theory is supported by the histologic findings in the abdominal wall, the urinary tract, and the male genital system. The abundance of fibrous tissue, collagen, and connective tissue with sparsely placed smooth muscle throughout the urinary tract indicates more of a mesodermal differentiation problem than one of obstruction.
The yolk-sac theory is based on the overdevelopment of the allantoic diverticulum that grows out from the yolk sac contiguous with the body stalk. If it becomes enlarged, it is incorporated into the urinary tract as a redundant enlarged urachus, bladder, and prostatic urethra. Unfortunately, this theory does not explain the abnormalities in the development of the upper urinary tract or male genital tract.
See Relevant Anatomy.
Pseudo–prune belly syndrome
Pseudo–prune belly syndrome, which is associated with prune belly syndrome uropathy, is characterized by normal abdominal wall examination findings and incomplete or absent cryptorchidism. In a study of 8 patients with this syndrome, 5 (63%) eventually developed renal failure. 
Prune belly–like variant
An abdominal wall defect commonly confused with prune belly syndrome has been termed prune belly–like variant. Some studies have reported abdominal wall defects without urologic anomalies. This defect involves only the abdominal wall muscles, in particular the internal and external obliques, as well as the transversalis muscles. In contrast with prune belly syndrome, the rectus muscles are not involved.
This defect causes weakness laterally, with bulging of the abdominal wall just below the rib cage. In such cases, CT scans of the abdominal wall reveal preservation of the rectus and obliques away from the area. The authors have surgically reconstructed two such defects in young male patients using a laparoscopic modification of the Firlit procedure, with excellent results. This syndrome may be associated with in utero distention of the abdominal cavity.
The patient pictured below had evidence of in utero megalocystis that resolved spontaneously.
Urethral obstruction should be addressed as soon as it is recognized. Progressive urethral dilation, as described by Passerini-Glazel et al, is the preferred method of treatment. Vesicostomy can also be an effective method of temporary diversion.
The literature contains little controversy regarding management of undescended testes in these children. If controversy or confusion arises, it concerns the optimal timing for the orchidopexy and which type of orchidopexy should be performed.
The management of the abdominal wall abnormalities is somewhat controversial. Some prefer no surgical reconstruction of the abdominal wall, while others advocate surgical reconstruction. The group that advocates surgical reconstruction is divided into 2 separate factions that support different techniques of abdominal wall reconstruction. The use of a rectus muscle transfer flap to the abdominal wall combined with an abdominal wall plication procedure can help ameliorate some of the back strain in many of these patients.
Reconstruction of the urinary tract also is controversial; some advocate prompt reconstruction, while others advocate a more passive approach and operate when necessary. Prune belly syndrome is characterized by elongated, dilated, and tortuous megaureters, which affect 81% of patients. Vesicoureteral reflux is common in these patients. Advocates of conservative treatment argue that, in a nonobstructive system with present suppressive therapy, intervention is not necessary. Those who argue for aggressive therapy in patients with prune belly syndrome point to Waldbaum and Marshall's review of 56 patients, in which 70% died and 16% were gravely ill.  Waldbaum and Marshall also argue for aggressive therapy when they point out that, "the purpose of the upper tract is to transport urine, not to store it."
Even with aggressive antibiotic therapy, urinary stasis and repeat infections may lead to inevitable loss of renal function. Regardless, ureteral reimplantation in patients with prune belly syndrome can be difficult and is frequently fraught with complications. To attest to this, the author has seen several patients who have previously undergone reimplantation but then developed ureteral strictures of the distal reimplanted ureters and required another reimplantation. Furthermore, reports in the literature have documented ureteral stenosis rates of up to 40% in tapered ureters.
Infravesical obstruction or obstruction at the prostatic urethra was originally thought to be due to a type I posterior urethral valve. This theory has been replaced by a new notion that the obstruction may be caused by severe angulation at the prostatic and membranous urethral junction. This may be due to a lack of striated muscle in the membranous urethra or urogenital diaphragm or a ring of obstructive tissue acting as a flap valve due to hypoplasia of the prostate, creating a ballooning of the prostatic urethra.
In these patients, studies have also shown that the smooth muscle in the prostate is reduced and the connective tissue content is increased, which may lead to a functional obstruction. This abnormality in the prostatic urethra can be similar to a valve created by anterior urethral diverticulum. Stephens describes this configuration as a type IV valve in patients with prune belly syndrome, in which the dilated prostatic urethra joins the membranous urethra in various configurations that cause obstruction.  However, these theories have not been supported by urodynamic studies, which fail to demonstrate either mechanical or functional outlet obstruction in most cases.
Studies indicate that the more distal lower ureter is abnormal in several ways, while the more proximal portion of the ureter is more anatomically normal. Histologically, the ureter has a smooth muscle deficiency with fibrous degeneration and a poor blood supply. In addition, a decrease in nerve plexuses is reported, with irregularity in degeneration of nonmyelinated Schwann fibers.
Herniation of the bladder is prevalent in patients with prune belly syndrome because the bladder is large and redundant. Patients with urethral obstruction commonly have a patent urachus, which enables the patient to survive; early deaths usually occur in those with urethral obstruction who do not have a patent urachus.
Some patients with prune belly syndrome have posterior urethral valves.
Prune belly syndrome is characterized by elongated, dilated, and tortuous megaureters, which affect 81% of patients.
Typically, patients with prune belly syndrome have megacystis. The bladder is routinely enlarged, although trabeculations are rarely present and muscular hypertrophy is inconsistent. The bladder can be fixed to the umbilicus via urachus, giving it an hourglass configuration radiographically. Bladder-voiding pressures are frequently near-normal, and residual urine volume is insignificant. Snyder et al describe a typical shift to the right, and some patients with prune belly syndrome can void normally.  Some authors feel that reduction cystoplasty can improve detrusor force. Some feel that the shape of the bladder in patients with prune belly syndrome can lead to unbalanced voiding and that a decreased bladder capacity would lead to increased detrusor efficiency based on Laplace law.
Anterior urethral abnormalities, which range from urethral atresia to megalourethra, are common in patients with prune belly syndrome. Patients who survive urethral atresia or microurethra have a patent urachus. Both scaphoid and fusiform megalourethra are associated with prune belly syndrome. The fusiform type is associated with deficient corpora cavernosa and more severe renal defects. Scaphoid megalourethra is associated with deficiency of the corpus spongiosum with a normal glans and fossa navicularis. The mesenchymal developmental arrest, which accounts for the major features of the syndrome, may also explain the urethral abnormalities.
Orthopedic anomalies are common and can affect 50% of patients. Scoliosis and congenital hip dislocations are common. Abnormalities associated with oligohydramnios also are observed.
Cardiac anomalies are reported in 10% of patients.
Alhawsawi et al reported a hepatic arterial aneurysm in a patient with prune belly syndrome. This is a rare defect that may be associated with inflammation or trauma to the arteries of the liver. Atherosclerosis, arthritis, and collagen vascular disease are the most common etiologies of inflammation that result in such aneurysms. The authors postulate that the mesodermal defect may account for the aneurysm. 
Gastrointestinal abnormalities, which include malrotation, atresia, stenosis, and volvulus, affect 30% of patients. All may be due to a persistence of the embryonic wide mesentery, with absent fixation to the posterior abdominal wall. The same defect allows the spleen to wander widely and can lead to splenic torsion. Imperforate anus, anorectal agenesis, omphalocele, and gastroschisis are uncommon but have been reported. Chronic constipation has been attributed to a decrease in abdominal wall pressure, which is necessary to aid in evacuation.
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